The Trump administration’s plans to overturn open internet protections face “a tsunami of resistance from a grassroots movement of Americans from every walk of life,” senators and activists warned on Wednesday.

Trump’s newly appointed Federal Communications Commission chairman Ajit Pai set out his plans to address internet regulation at a speech in Washington on Wednesday. Pai has vowed to take “fire up the weed-whacker” and cut Obama-era rules meant to enforce an open internet where all traffic is treated equally online – the so-called net neutrality rules.

Pai and the cable companies want a more flexible system and lighter regulation, where internet service providers volunteer to protect net neutrality. They argue that the rules are hampering investment.

Pai said he hoped to “return to the light-touch regulatory framework that served our nation so well during the Clinton administration, Bush administration, and the first six years of the Obama administration.”

In a press conference before Pai’s speech, senators Edward Markey, Richard Blumenthal and Ron Wyden were joined by internet activists to warn Pai and Trump that efforts to undermine the rules would be met with stiff resistance.

In 2015, after a heated public battle, activists pushed the FCC to establish tough new rules that bar internet service providers from creating fast lanes, or “throttling” online traffic in a way that could allow them to pick online winners and losers and stifle competition.

Senator Markey said: “Just two years ago the Federal Communications Commission listened to four million voices and adopted strong net neutrality rules. Those rules ensured that the internet would remain a level playing field for everyone, making the internet America’s foundation for information and commerce and communications. We are on the right side of history and I’m ready for this fight to come.”

Craig Aaron, president of consumer-advocacy group Free Press, said the Trump’s administration was trying to erase “one of the most important public interest victories ever.” Such a move would leave consumers “at the mercy of the phone and cable companies, some of the most hated companies in America.”

Aaron said Pai was living in a “fantasy world, where all will be fine if internet companies double-pinky swear not to interfere with online pathways and portals – despite their long history of doing just that.”

The previous battle over net neutrality led to a massive outpouring of public support. Activists organised protest camps outside and bombarded Congress with calls. Comedian John Oliver’s dissection of the debate has now been viewed more than 12m times on YouTube.

Evan Greer, the campaign director for Fight For the Future, said that many supporters of net neutrality were also Trump supporters. “Donald Trump has completely misjudged his base on this issue,” Greer said. “People from across the political spectrum want to keep the internet free from throttling and censorship. They don’t want their cable companies, who they already pay too much money to connect them to the internet, to decide what they can do and see online.”